Thermoplastic thermoformable composite material and method of forming such material

ABSTRACT

A thermoplastic resin defines a core of a thermoformable thermoplastic composite material. The core is sufficiently thick to provide for a shaping of the composite material at an elevated temperature to any desired configuration. First and second layers of fabric material are disposed on opposite sides of the core. The fabric material may be formed of glass, carbon or aramid and may be formed from woven fibers, unidirectional or chopped fibers or random strand mats. The fabric layers have a thickness sufficient to impart strength and rigidity to the fabric material. Layers of a thermoplastic thermoformable resin material may be disposed on the layers of the fabric material. The thermoplastic layers impregnate the fabric layers, bond the fabric layers to the core and provide a smooth external surface to the composite material. The thermoplastic layers are of a sufficient thickness to maximize the flexural load strength of the composite material and to eliminate the formation of any rippling or buckling of the composite material. The core and the additional resin layers may be an acrylic, a polycarbonate or ABS. The core may be thicker than the combined thicknesses of the fabric layers and the thermoplastic layers. For example, each of the fabric layers may have a thickness in the order of eight mils (0.008&#34;) to nine mils (0.009&#34;). The thickness of each of the thermoplastic layers may be in the order of seven mils (0.007&#34;) to nine mils (0.009&#34;). The thickness of the thermoplastic composite material may be in the order of eighty five mils (0.085&#34;) to one hundred and twenty five mils (0.125&#34;).

This is a division, of application Ser. No. 07/731,640, now U.S. Pat.No. 5,354,604.

This invention relates to a thermoformable thermoplastic compositematerial which is strong and light and which is capable of beingthermally deformed to any desired shape without buckling or rippling ofthe composite material.

It is often desirable to form a sheet of plastic material into a complexshape without any rippling or buckling of the material. It is alsodesirable to make such sheet as light (from a weight standpoint), thinand strong as possible. It is also desirable to form a sheet with theabove characteristics into the complex shape in a relatively simpleprocess so that the costs of providing the complex shape in the sheetare low and so that the yield of the final product is high.

A sheet with the properties discussed may have a wide variety ofdifferent uses. For example, it may be shaped to conform to the shape ofa foot. Alternatively, the sheet may be shaped to provide an archsupport in a shoe. As another example, the sheet may be shaped to bedisposed as a spring element in the sole of a wearer's shoe. Althoughthe examples have been limited to uses in shoes, this is only one of anumber of different fields or areas in which such material can be used.

Thermoplastic materials have been used to provide sheets with theproperties discussed above. To obtain a desired shape, a mold isprovided with the desired shape. The thermoplastic material is thenformed into the desired shape by applying heat and pressure to thethermoplastic material to move the material into the mold and to havethe material adopt the configuration of the mold. Suitable thermoplasticmaterials for forming into complex shapes may be any suitablethermoplastic material such as acrylics, polypropylenes andpolyethylenes.

Thermoplastic materials are advantageous because they can be reshaped ifit is desired to change the configuration somewhat after the materialhas been initially shaped through the application of heat and pressure.However, thermoplastic materials are distinctly disadvantageous in thatthey have to be provided with a considerable thickness in order toprovide the necessary rigidity in such applications as orthotics. Forexample, thicknesses of 0.120" to 0.200" may be required. Unfortunately,such thick materials are heavy and are generally too thick to bedisposed in foot gear. Furthermore, the thermoplastic materials are notas durable and resistant to breaking as would otherwise be required. Thethermoplastic materials also sometimes buckle and ripple when they aretransformed into complex shapes.

Thermosetting materials have also been used to provide complex shapessuch as for footwear and orthotic applications. An advantage of athermosetting material is that it can be made quite thin to obtain thedesired shape. For example, the thickness of tile thermosetting materialmay be in the order of 0.065" to 0.080". One problem with shapingthermosetting materials into complex shapes is that the thermosettingmaterials have to be shaped properly the first time. The reason is thatthe thermosetting materials cannot be reshaped after they have beenheated to a temperature for initially shaping the material. This problemhas severely limited the use of the thermosetting material to providecomplex shapes. Another problem often is that the thermosetting materialtends to be heavy even though it is thin.

Until recently, because of the problems discussed above forthermosetting materials, complex shapes such as for orthotic insertshave generally been formed from thermoplastic materials such as acrylicsand polypropylenes. The orthotic inserts have been formed by initiallymaking a plaster mold from the patient's foot. This plaster mold hasformed a negative image of the patient's foot. A positive mold has thenbeen made from the negative plaster mold. Thermoplastic material hasthen been transformed into the desired shape by using heat and pressureto conform the thermoplastic material to the positive mold.

U.S. Pat. No. 4,778,717 issued to me on Oct. 18, 1988, for a"Thermoplastic Thermoformable Composite Material" and assigned of recordto the assignee of record of this application discloses and claims acomposite thermoplastic material which can be easily formed, and evenreformed if necessary, at elevated temperatures to any desired complexshape. The composite material is light and strong and is able to bethermally deformed, and even reformed, to any desired shape withrelatively minimal buckling or rippling. U.S. Pat. No. 4,778,717 is madeof reference to provide a background for the improvement constitutingthis invention and also to complete any disclosure in this applicationof the construction and formation of the composite material.

The composite material of U.S. Pat. No. 4,778,717 is formed from a corematerial of a thermoplastic resin material and a pair of layers offabric material disposed on the opposite sides of the core material.Layers of a thermoplastic material envelope and impregnate the layers ofthe fabric material and bonds the layers of the fabric material to thecore. The layers of the fabric material have a total thicknesssufficient to impart strength and rigidity to the composite material.The core is of a sufficient thickness to provide for a shaping of thecomposite thermoplastic material at an elevated temperature to anydesired shape or configuration with relatively little rippling orbuckling of the fabric material. The composite material of U.S. Pat. No.4,778,717 has received widespread acceptance for orthotics.

This invention provides a thermoplastic thermoformable compositematerial which constitutes an improvement over the composite material ofU.S. Pat. No. 4,778,717. In one embodiment of the invention, athermoplastic thermoformable resin material defines a core of athermoformable thermoplastic composite material. The core issufficiently thick to provide for a shaping of the composite material atan elevated temperature to any desired configuration.

First and second layers of fabric material are respectively disposed onopposite sides of the core. The fabric material may be formed of glass,carbon or aramid and may be formed from woven fibers, unidirectional orchopped fibers or random strand mats. The fabric layers have a totalthickness sufficient to impart strength and rigidity to the compositematerial.

Layers of a thermoplastic thermoformable resin material may be disposedon the outer layers of the fabric material. The thermoplastic layersimpregnate the fabric layers, bond the fabric layers to the core andprovide a smooth external surface to the composite material. Thethermoplastic layers are of a sufficient thickness to maximize the loadto bend of the composite material and to eliminate the formation ofrippling or buckling of the composite material.

The core may be preferably thicker than the combined thicknesses of thefabric layers and the thermoplastic layers. For example, each of tilefabric layers may have a thickness in the order of eight mils (0.008")to nine mils (0.009"). The thickness of each of the thermoplastic layersmay be in the order of seven mils (0.007") to nine mils (0.009"). Thetotal thickness of the thermoplastic composite material may be in theorder of eighty mils (0.080") to one hundred and twenty five mils(0.125").

In the drawings:

FIG. 1 is a schematic perspective view, partially broken away, of acompleted orthotic insert constructed from a thermoplasticthermoformable composite material in accordance with tile teachings ofthis invention;

FIG. 2 is a bottom plan view of the orthotic insert of FIG. 1;

FIG. 3 is an enlarged exploded fragmentary schematic perspective view ofthe various materials used to form the thermoplastic thermoformablecomposite material constituting this invention;

FIG. 4 is a fragmentary schematic perspective view of the thermoplasticcomposite material of this invention in sheet form;

FIG. 5 is a bottom plan view illustrating a portion of the sheetmaterial of FIG. 4 after trimming of the sheet material to a desiredconfiguration but prior to the formation of the sheet material into thecomplex shape shown in FIGS. 1 and 2;

FIG. 6 is a bottom plan view illustrating the forming of the sheetmaterial of FIG. 5 into the complex shape shown in FIGS. 1 and 2 butprior to the other steps to complete the orthotic insert shown in FIGS.1 and 2;

FIG. 7 is a view schematically illustrating a method of forming thethermoplastic sheet material shown in FIG. 4;

FIG. 8 is a graph schematically illustrating the relationship betweenthe increase in the flexural strength of the thermoplastic compositematerial with progressively increased thicknesses of layers of thethermoplastic material in the composite material;

FIG. 9 is a graph schematically illustrating the relationship betweenthe abrasion life of the composite material with progressively increasedthicknesses of the layers of the thermoplastic material; and

FIG. 10 is a graph schematically illustrating how instances of ripplingand buckling of the composite material are progressively reduced to avalue of zero (0) with progressively increased thicknesses of the layersof the thermoplastic material.

FIG. 4 illustrates a thermoplastic thermoformable composite materialgenerally indicated at 10 and constituting one embodiment of thisinvention. The composite material 10 includes a pair of layers 12 and 14of a fabric material, preferably woven. The material for the fabriclayers 12 and 14 may be made from fibers of a suitable material such ascarbon, glass or aramid or a combination of these materials. The layers12 and 14 may be formed from woven fibers, unidirectional or choppedfibers or continuous random strand mats. It will be appreciated thatother materials or combinations of materials may also be used. Each ofthe layers 12 and 14 may be relatively thin. For example, the layers 12and 14 may have a suitable thickness in the order of eight thousandthsof an inch (0.008") to nine thousandths of an inch (0.009").

The composite material 10 also includes a core 16 made from a suitablethermoplastic thermoformable material (a resin). A suitable resin may bean acrylic although other thermoplastic composite materials such as apolycarbonate or ABS may be used. The core 16 is disposed between thelayers 12 and 14 of the fabric material. The thickness of the core 16 ispreferably considerably greater than the total thickness of the layers12 and 14 of the fabric material. For example, the total thickness ofthe core 16 and the layers 12 and 14 of the fabric material may beapproximately seventy thousandths of an inch (0.070") when each of thelayers 12 and 14 has a thickness in the order of 0.008" to 0.009".

As a first step in forming the composite material 10, the layer 12 ofthe fabric material is disposed against the core 16 on one side of thecore. The layer 14 of fabric material is thereafter disposed against thecore 16 on the other side of the core. As will be seen in FIG. 7, thelayers 12, 14 and 16 may be disposed in the relationship described aboveby unwinding the core 16 and the layers 12 and 14 from rolls of materialon a synchronized basis.

Although a preferred embodiment of the composite material has beendescribed above, it will be appreciated that the thickness of thedifferent layers of material can be varied through a wide range withoutdeparting from the scope of the invention. For example, the totalthickness or volume of all of the different layers of fiber or fabricrelative to the thickness of the core 16 may be between approximatelyfive percent (5%) and one third (1/3). The thickness or volume of thelayers 12 and 14 of the fiber or fabric relative to the total thicknessof the composite material 10 is dependent upon the use to be made of thecomposite material. For example, when the composite material is to beused for an orthotic insert, the thickness of the layers 12 and 14 offabric or fiber relative to the thickness of the core 16 in thecomposite material 10 may be approximately twenty five percent (25%) asdescribed above.

Additional layers 18 and 20 (FIGS. 4 and 7) of a thermoplasticthermoformable resin material such as an acrylic may be respectivelydisposed on the layers 12 and 14 of the fabric material. The layers ofthe thermoplastic thermoformable resin material 18 and 20 respectivelyenvelop and impregnate the layers 12 and 14 of fabric material. Each ofthe layers 18 and 20 preferably has a thickness in the order of sevenmils (0.007") to nine mils (0.009"). Each of the layers 18 and 20respectively envelopes and impregnates the contiguous layers 12 and 14of fabric material and bonds the layers of fabric material to the core16.

The material of the layers 18 and 20 of resin material may be the sameas, or different from, the material of the core 16. However, if thematerial of the layers 18 and 20 is different from the material of thecore 16, the different materials have to be compatible so that they willform a unitary whole when extruded or molded into the composite material10.

As will be appreciated, the layers 18 and 20 of thermoplastic materialare significantly thicker than corresponding layers of thermoplasticmaterial in the thermoplastic composite material of U.S. Pat. No.4,778,177. As will be described subsequently, this increased thicknessin the layers 18 and 20 offers significant advantages in thethermoplastic composite material of this invention over thethermoplastic composite material of U.S. Pat. No. 4,778,177.

As shown in FIG. 8, the flexural load of the thermoplastic compositematerial increases linearly with increased thicknesses in thethermoplastic layers 18 and 20 until a thickness of approximately sevenmils (0.007") in such layers. At such thicknesses and at increasedthicknesses above a value of approximately seven mils (0.007") for eachof the layers 18 and 20, the flexural strength of the thermoplasticcomposite material 10 remains substantially constant. This increasedflexural strength is often important in such articles as arch supportsfor shoes since the arch supports are subjected to great flexural loadsas a result of the weight of an individual wearing shoes with such archsupports and as a result of the forces imposed upon such arch supportswhen such individual walks or runs.

FIG. 10 illustrates the tendency of the thermoplastic composite material10 to wrinkle or buckle when the material 10 is shaped at elevatedtemperatures to form an article such as an arch support in a shoe. Aswill be seen, the tendency of the material 10 to wrinkle or buckle insuch shaping decreases with progressive thicknesses in the layers 18 and20 of thermoplastic material until a thickness of approximately sevenmils (0.007"). At such thicknesses and at thicknesses above seven mils(0.007"), there is no tendency for the thermoplastic composite material10 to wrinkle or buckle when it is shaped at elevated temperatures.

It has been found that the layers of thermoplastic material covering thelayers of fabric material in the thermoplastic composite material ofU.S. Pat. No. 4,778,177 tends to wear when it is subjected to abrasion.For example, when the thermoplastic composite material is shaped into anarch support, the wearer's foot tends to force the outer layers ofthermoplastic resin to be abraded by the shoe when the individual walksor runs. As shown in FIG. 9, the life of the outer layers ofthermoplastic resin tends to increase linearly with progressiveincreases in the thickness of the layers. By providing each of thelayers 18 and 20 with a thickness in the order of seven mils (0.007") tonine mils (0.009"), the life of the layers is significantly enhancedbefore the layers become worn by abrasion to expose the layers 12 and 14of fabric material.

During the formation of the different layers of the fabric materials andthe resin material into the composite material 10 as by laminating ormolding the different layers, the additional layers 18 and 20 tend tofacilitate the impregnation and encapsulation of the layers 12 and 14 offabric material. Furthermore, they tend to cover the layers 14 and 16 offabric material and provide a smooth external surface to these layers.

The layers 12 and 14 of the fabric material, the core 16 and the layers18 and 20 of the thermoplastic material are then laminated into a thinsheet of the composite material at a suitable temperature and pressureas shown in FIG. 7.

FIG. 7 shows the additional layers 18 and 20 as being sprayed on thefabric layers 12 and 14. However, it will be appreciated that the layers18 and 20 may be applied in different ways, such as in solid layers, onthe fabric.

The particular temperature and pressure for providing the lamination ofthe different layers are dependent upon a number of parameters includingthe specific materials used for each of the layers 12, 14, 18 and 20 andthe particular material used for the core 16. The particular temperatureand pressure are also dependent upon the specific thickness of each ofthe layers 12, 14, 18 and 20 and the core 16 and the thickness of eachof the layers relative to the thickness of the other layers. Althoughthe formation of the composite material 10 by a laminating process ispreferred, the composite material may also be suitably formed as by amolding process.

As an illustrative example, assume that the core 16 is approximatelyfifty thousands of an inch (0.050") thick and the composite material 10is approximately eighty thousandths of an inch (0.080") thick. Furtherassume that the core 16 is an acrylic and the layers 12 and 14 of fabricmaterial are made from a carbon woven fabric as described above. Undersuch circumstances, the composite material 10 may be initially laminatedfor a period of approximately two (2) to three (3) minutes at a pressureprogressively increasing between zero pounds per square inch (0 psi) andten pounds per square inch (10 psi). The composite material 10 may thenbe laminated for two (2) to three (3) minutes at a pressureprogressively increasing to approximately ninety pounds per square inch(90 psi). The composite material may subsequently be laminated forapproximately thirty (30) minutes at a pressure progressively increasingto a value in the range of three hundred to four hundred pounds persquare inch (300-400 psi).

After the composite material 10 has been laminated as described in theprevious paragraph, the composite material may be annealed. Theannealing cycle may be dependent upon the parameters of the compositematerial such as those specified two (2) paragraphs previously. Forexample, under the circumstances described in the previous paragraph, anannealing cycle may be provided for a period of approximately sixty (60)hours. In this annealing cycle, the composite material may be annealedat a suitable temperature such as approximately 180° F. for a suitableperiod such as approximately ten (10) hours, then at a suitabletemperature such as approximately 212° F. for a suitable period such asapproximately eight (8) hours, then ramped to approximately 225° F overa period of approximately ten (10) hours, then held at the temperatureof approximately 225° F. for a period of approximately ten (10) hours,thereafter at a suitable temperature such as approximately 250° F. for asuitable period such as approximately four (4) hours and finally at asuitable temperature such as approximately 260° F. for the remainingperiod such as approximately eighteen (18) hours. The composite material10 may then be cooled to ambient temperatures.

The annealing of the composite material 10 after the lamination of thecomposite material under heat and pressure offers certain importantadvantages. By annealing the composite material 10, moisture in thecomposite material 10 is eliminated. This prevents pockets of foreignmaterial such as water from remaining in the composite material 10 afterthe formation of the composite material. Such foreign pockets areundesirable because they limit the ability of the composite material tobe formed into complex shapes without rippling or bucking. The annealingof the composing material is also advantageous because it eliminatesunreacted monomers and causes all of such unreacted monomers to beconverted to polymers.

Although the thickness of the core 16 is preferably greater than theaggregate thickness of the layers 12 and 14 and the thermoplastic layers18 and 20, it will be appreciated that the thickness of the core 16 maybe equal to, or less than, the aggregate thickness of the other layers.For example, the thickness of the core 16 may be decreased below thethickness of the other layers when it is desired to provide thecomposite material 10 with compliant properties.

When the composite material 10 has been formed into sheets as describedabove and is thereafter to be converted into a complex shape, thematerial may be disposed in a mold having the desired shape and may besubjected to a suitable temperature and pressure to move the sheet intoconformity with the shape of the mold. The composite material 10 hascertain distinct advantages while it is being formed into the desiredshape and after it has been so formed. During such formation, the layers12 and 14 of the fabric material provide a body to the compositematerial. The core 16 provides for a movement between the layer 12 onone side of the core independently of the movement of the layer 14 onthe other side of the core.

In this way, the composite material 10 can be formed into any desiredshape without any rippling or buckling of the composite material or thefabric material. This is important in insuring that the compositematerial 10 will occupy only a minimal amount of space and will becomfortable to the user such as when it is formed into an orthoticinsert. It is also important in insuring that the composite material 10will have an optimal flexural strength, stiffness and rigidity after ithas been formed into the desired shape.

The flexural load, stiffness and rigidity of the composite material 10may be controlled dependent upon the total thickness of the layers 12and 14 of the fabric material relative to the total thickness of thecomposite material. For example, as the total thickness of the layers 12and 14 of the fabric material increases relative to the total thicknessof the composite material 10, the stiffness, load and rigidity of thecomposite material 10 tend to be enhanced while the ability of thecomposite material to be conformed to complex shapes tends to bereduced. When the composite material 10 is formed as described above,the thermoplastic material of the layers 18 and 20 encapsulates andimpregnates the fabric or fibers in the layers 12 and 14 of the fabricmaterial and bonds the fabric or fibers to the core 16.

FIGS. 1 and 2 schematically show an orthotic insert generallyillustrated at 30. The orthotic insert includes a base member 32 whichis made from the composite material 10 and which is transformed to thedesired shape after being provided in sheet form. A heel portion 34 isattached to the base member 32. The heel portion 34 may be made in aconventional manner. The heel portion 34 may be molded from a rigidplastic material to operate as a heel support. A soft durable covering36 covers the base member 32. The soft durable covering material 36 maybe made from any suitable leather-like material to provide for acomfortable surface adjacent the foot of the orthotic user.

FIG. 1 also illustrates that the base member 32 formed from thecomposite material 10 has a complex shape conforming to the bottomsurface of the foot of the user of the orthotic insert 30. Each suchorthotic insert 30 has to be made for an individual user because of itscomplex shape. In general, such orthotic inserts are provided by medicalpersonnel who specialize in fitting such inserts to a user to providethe proper support to the user during various activities.

Typically, plaster molds of the user's feet are made and sent to alaboratory. The laboratory then makes castings from the molds. Thecastings thereby represent the bottoms of the user's feet. Orthoticinserts are then formed to provide for the proper inserts conforming tothe bottom of the user's feet. These orthotic inserts constitutefinished products. However, it is important that these orthotic insertsbe post formable so that adjustments in their shape can be made in thefield if there are any problems with the inserts after the inserts havebeen applied to the user's feet. The formation of the base member 32from the composite material 10 allows for such post forming.

Although this invention has been disclosed and illustrated withreference to particular embodiments, the principles involved aresusceptible for use in numerous other embodiments which will be apparentto persons skilled in the art. The invention is, therefore, to belimited only as indicated by the scope of the appended claims.

We claim:
 1. In combination in a thermoplastic thermoformable compositematerial having properties of being shaped into a complex non-planarform without rippling or buckling,a core of a thermoplastic material, alayer of a fabric material positioned on one side of the core, and alayer of a thermoplastic material bonding the layer of the fabricmaterial to the core and enveloping and impregnating the layer of thefabric material and having a thickness relative to the layer of thefabric material to provide for the shaping of the composite material atelevated temperatures without any any rippling or buckling of any layersin the thermoplastic composite material and impart strength and rigidityto the composite material and to maximize the flexural load of thethermoplastic composite material, the thermoplastic material in thelayer being the same as or compatible with the thermoplastic material inthe core, the layer of the fabric material producing a stiffness andrigidity of the thermoplastic composite material after such shaping, thecore of the thermoplastic composite material facilitating the shaping ofthe composite material into the complex form.
 2. In a combination as setforth in claim 1,the layer of the fabric material being selected fromthe group consisting of woven threads, unidirectional fibers and randomstrand mats.
 3. In a combination as set forth in claim 2,the layer ofthe fabric material being selected from the group consisting of carbon,glass and aramid.
 4. In a combination as set forth in claim 1,the layerof the fabric material having a thickness in the order of eight mils(0.008") the nine mils (0.009").
 5. In a combination as set forth inclaim 3,the layer of the fabric material having a thickness in the orderof eight mils (0.008") to nine mils (0.009"), the layer of thethermoplastic material having a thickness in the order of seven mils(0.007") to nine mils (0.009").
 6. In a combination as set forth inclaim 5,the layer of the fabric material being selected from the groupconsisting of woven threads, unidirectional fibers and random strandmats.
 7. In a combination as set forth in claim 6,the layer of thefabric material being selected from the group consisting of carbon,glass and aramid, the layer of the thermoplastic material being selectedfrom the group consisting of acrylic, polycarbonate and ABS.
 8. In acombination as set forth in claim 2,the layer of the fabric materialbeing selected from the group consisting of carbon, glass and aramid,the layer of the thermoplastic material being selected from the groupconsisting of acrylic, polycarbonate and ABS.
 9. A thermoplasticthermoformable composite material as set forth in claim 8 whereinthethermoplastic core and the additional layer of the thermoplasticmaterial are made from a material selected from the group consisting ofan acrylic, a polycarbonate and ABS.
 10. A thermoplastic thermoformablecomposite material as set forth in claim 8 whereinthe thermoplastic coreis made from a material selected from the group consisting of anacrylic, a polycarbonate and ABS.
 11. A thermoplastic thermoformablecomposite material as set forth in claim 8 whereinthe layer of thefabric material is selected from the group consisting of carbon, glassand aramid.